How do you keep people from grabbing you when you are swamped? Do you sit down with them and have a quiet, reasoned discussion, explaining why you are sometimes too busy for them? Do you dash on, yelling "sorry, not now!" or "gerroff!"? If so, do you explain later by e-mail, in person, or not at all? Do you stop and stare, say it's rude, threaten mayhem?
Most important: Does it work? Do you ever get grabbed by the same person again? If so, is it only in exigent situations or also for non-emergencies that they grab you?